How to adjust the water level in a toilet cistern

The importance of maintaining water levels in toilet cisterns

Keeping the correct water level in your toilet cistern is essential for both efficiency and hygiene.

If the water level is too low, it may not effectively flush waste, leading to a blocked toilet and unpleasant odours. On the other hand, if it’s too high, it can cause continuous running, wasting water, and raising utility bills.

Maintaining the proper level ensures your toilet operates smoothly, reduces the risk of plumbing issues, and supports water conservation efforts.

Low water levels

When the water level in your toilet cistern is too low, it can lead to all kinds of annoying problems.

For starters, the toilet’s flush might not be strong enough to clear everything out, which can cause clogs and leave you flushing more than once. It can also leave parts of the cistern exposed, making it easier for stains and mineral buildup to form. And without enough water to block sewer gases, you might even notice some unpleasant smells coming from your toilet.

High water levels

If the water level in your toilet cistern is too high, it can create just as many issues as low water levels.

One big concern is the risk of overflowing. Too much water can also lead to constant running or refilling, which wastes water and can drive up your utility bills. Not only is that bad for your wallet, it’s also not great for the environment.

Safety considerations

Before making any adjustments, be sure you know how to turn off the toilet’s water supply using the shut-off valve—usually located behind or beside the toilet—in case of an emergency.

Also, avoid taking apart the fill valve, as it’s a delicate component that can be easily damaged. To stay safe, stick to the built-in adjustment features designed for simple fixes.

What you'll need to adjust the water level in your toilet

To adjust the water level in your toilet, you’ll need just a few simple tools:

• A flathead screwdriver for float or fill valve adjustments
• Rubber gloves, optional, but helpful for cleanliness
• A towel or small bucket, in case of minor spills

How to adjust the water level in a toilet cistern

To keep your toilet working properly, the water level inside the cistern should sit about an inch below the overflow tube.

Adjusting a ball-and-arm float

A ball-and-arm float is one of the most common and oldest toilet fill mechanisms. It’s easy to spot (it looks like a round ball attached to a metal arm inside the cistern). Here's how to adjust it:

1. Lift the cistern lid and place it safely aside.
2. Check the water level.
3. Turn off the water supply to the toilet.
4. Find the adjustment screw on top of the fill valve, where the arm connects.
5. Turn the screw clockwise to raise the water level or anticlockwise to lower it.
6. Turn the water supply to the toilet back on.
7. Flush the toilet and see where the water settles. Repeat adjustments if needed.

Adjusting a cylinder float

Cylinder floats, also known as float cups, are common in modern toilets. Instead of a ball on an arm, you’ll see a plastic cup that moves up and down along the fill valve shaft. Here’s how to adjust it:

1. Remove the cistern lid and set it aside carefully.
2. Locate the float adjustment stem, which is a long plastic rod or a screw-like mechanism on the side of the fill valve.
3. Turn off the water supply to the toilet.
4. Pinch or turn the adjustment clip or screw (depending on your model).
1. For clip types, pinch the clip and slide the float up to raise the water level or down to lower it.
2. For screw types, turn the screw clockwise to lower the float or counterclockwise to raise it.
5. Turn the water supply to the toilet back on.
6. Flush the toilet to test the new level and make further adjustments as needed.

Installing a new fill valve

If adjusting the float doesn’t fix the issue, your fill valve might be worn out and need replacing. Here’s how to do it:

1. Turn off the water supply to the toilet.
2. Empty the cistern by flushing the toilet, then use a towel or sponge to soak up any remaining water.
3. Remove the old fill valve by unscrewing the locknut underneath the cistern.
4. Install the new fill valve by inserting it through the hole and securing it with the new locknut.
5. Turn the water supply to the toilet back on, let the cistern fill, and check for leaks.
6. Adjust the new float to the correct water level if needed (usually 1 inch below the overflow tube).

How to keep the water level in the right place

Once you’ve adjusted your toilet’s water level, a little upkeep can go a long way in keeping it steady. All it takes is a few easy tips to help maintain the right water level over time:

• Check for leaks regularly. A slow leak can cause the water level to drop without you noticing.
• Inspect the cistern water level every few weeks. Make sure it’s still about an inch below the overflow tube.
• Clear clogs promptly: A clog in the toilet or drain can disrupt water levels and lead to overflow.
• Replace worn or faulty fill valves if you notice inconsistent water levels or hear constant running.
• Listen for unusual sounds, like running water or hissing, which may indicate a problem with the float or valve.

With a few simple checks, you can avoid bigger issues and keep your toilet working efficiently.

Plumbing you can rely on

While adjusting your toilet’s water level is a simple fix, some plumbing problems need a professional. That’s where HomeServe comes in. Whether it’s a leak, clog, or faulty part, our trusted team is ready to help quickly and professionally.

For added peace of mind, our Plumbing and Drainage Cover is here to help avoid the stress of unexpected repairs. Reliable plumbing help is always just a call away.